Polyurethane coating materials typically comprise a catalyst, and in this context not only acidic compounds but also, in particular, tertiary amines and/or metallic compounds, such as various tin compounds, for example, more particularly dibutyltin dilaurate and dibutyltin oxide, are employed.
The employment of tin-containing catalysts is to be avoided in coating materials, as elsewhere, because of the toxicity inherent in many tin compounds. The EU Commission's Working Group on Classification and Labelling” have categorized dibutyltin oxide (DBTO) and dibutyltin dilaurate (DBTL) accordingly.
The article available on the Internet at the address www.wernerblank.com and titled “Catalysis of the Isocyanate-Hydroxyl Reaction by Non-Tin Catalysts” by Werner J. Blank, Z. A. He and Ed. T. Hessell from the company King Industries Inc. therefore describes alternatives to the customary tin-containing catalysts based on various metal salts and metal complexes, such as zirconium chelates, aluminum chelate, and bismuth carboxylate.
DE 10 2008 061 329 A1 and WO 09/135600 disclose coating materials where the use of metallic catalysts is to be avoided as far as possible and which instead comprise, as catalyst, 1,3-substituted imidazolium salts for the deblocking of blocked polyisocyanates in polyurethane coating materials.
WO04/029121 describes polyurethane compositions which are stabilized in terms of the reactivity of the composition by addition of acids with a pKa range between 2.8 and 4.5, these acids being able to be utilized at the same time as catalyst. Acids used in this context and with a pKa range between 2.8 and 4.5 include, for example, benzoic acid, hydroxybenzoic acid, salicylic acid, phthalic acid, and so on. The compositions preferably comprise no further catalyst, although in addition it is also possible to use the typical known polyurethane catalysts, such as tertiary amines or amidines or organometallic compounds, such as tin compounds more particularly. Where amines are used as catalyst, it is necessary to employ great care in the selection of the type of amine and its amount, since the aminic catalysts are able in part to eliminate the stabilizing action of the organic acids added.
Furthermore, U.S. Pat. No. 7,485,729 B2 and also the equivalent specifications WO06/022899, US 2006/0247341 A1 and US 2009/0011124 A1, describe organometallic compounds and coating materials comprising them. Coating materials described are powder coating materials based on hydroxyl-containing polyacrylates and/or polyesters and on uretdione-group-containing polyisocyanates; liquid paints based on hydroxyl-containing polyacrylates and/or polyesters and on blocked polyisocyanates; and solventborne coating materials based on epoxy/carboxyl and/or epoxy/anhydride components. The organometallic compounds used as catalysts are, in addition to other metal-amidine complexes, cyclic or acyclic zinc biscarboxylate-bis-amidine complexes, such as, for example, Zn(1,1,3,3-tetramethylguanidine)2 (2-ethylhexanoate)2.
Furthermore, WO 2001/98393, WO08/74491, WO 08/74490, WO 08/74489, WO09/077181 and WO 10/149236 disclose coating material compositions which comprise at least one hydroxyl-containing compound (A), at least one compound (B) containing isocyanate groups and silane groups, and a catalyst suitable for the crosslinking of the silane groups. Catalysts used are phosphorus-containing catalysts, more particularly phosphorus- and nitrogen-containing catalysts. These coating material compositions have the advantage over conventional polyurethane coating materials of a significantly enhanced scratch resistance in conjunction with good weathering stability.
Further, EP-A-1 273 640 describes 2-component coating materials comprising a polyol component and a crosslinker component, consisting of aliphatic and/or cycloaliphatic polyisocyanates or the polyisocyanates derived from them by polymerization, allophanatization, biuretization or urethaneization, where 0.1 to 95 mol % of the originally free isocyanate groups present have reacted with bisalkoxysilylamine.
Finally, PCT patent applications PCT/EP2012/052284, PCT/EP2012/051444, PCT/EP2012/051574, PCT/EP2012/054546, not yet laid open, and European patent application No. 12152406.0, not yet laid open, describe coating material compositions which as well as at least one polyhydroxyl group-containing compound (A), at least one polyisocyanate group-containing compound (B) and at least one catalyst (D) based on a zinc-amidine complex, also comprise at least one monomeric aromatic, optionally substituted carboxylic acid (S), whose carboxyl group is conjugated with a π-electron system.